(1) Field of the Invention
The invention relates to a device for vial opening comprising an external container, in which a closed vial having a vial body and a vial head is arranged, and comprising a hollow space in the region of the vial head, whereby the hollow space comprises at least one opening and a connection to the vial.
Accordingly, the invention provides a robust device for storing and opening monomer vials of vacuum cementing systems for polymethylmethacrylate bone cements that are pre-filled with cement powder and monomer liquid and are provided to the medical user in the form of full-prepack vacuum cementing systems.
(2) Description of Related Art
Conventional PMMA bone cements have been known for decades and are based on the ground-breaking work of Sir Charnley (Charnley, J.: Anchorage of the femoral head prosthesis of the shaft of the femur. J. Bone Joint Surg. 42 (1960) 28-30). The basic structure of PMMA bone cements has remained the same ever since. PMMA bone cements consist of a liquid monomer component and a powder component. The monomer component generally contains the monomer, methylmethacrylate, and an activator (N,N-dimethyl-p-toluidine) dissolved therein. The powder component consists of one or more polymers that are made by polymerisation, preferably suspension polymerisation, based on methylmethacrylate and co-monomers, such as styrene, methylacrylate or similar monomers, a radio-opaquer, and the initiator, dibenzoylperoxide. Mixing the powder component and the monomer component, a dough that can be shaped plastically is generated by swelling of the polymers of the powder component swell in the methylmethacrylate. Mixing the powder component and the monomer component, the activator, N,N-dimethyl-p-toluidine, reacts with dibenzoylperoxide while forming radicals. The radicals thus formed trigger the radical polymerisation of the methylmethacrylate. Upon advancing polymerisation of the methylmethacrylate, the viscosity of the cement dough increases until the cement dough solidifies.
Polymethylmethacrylate bone cements can be mixed by mixing the cement powder and the monomer liquid in suitable mixing beakers with the aid of spatulas. This procedure is disadvantageous in that air inclusions may be present in the cement dough thus formed and cause destabilisation of the bone cement later on. For this reason, it is preferred to mix bone cement powder and monomer liquid in vacuum mixing systems, since mixing in a vacuum removes air inclusions from the cement dough to a large extent and thus achieves optimal cement quality (Breusch S J et al.: Der Stand der Zementiertechnik in Deutschland. Z Orthop. 1999, 137: 101-07). Bone cements mixed in a vacuum have clearly reduced porosity and thus show improved mechanical properties. A large number of vacuum cementing systems has been disclosed of which the following shall be listed for exemplary purposes: U.S. Pat. No. 5,624,184, U.S. Pat. No. 4,671,263, U.S. Pat. No. 4,973,168, U.S. Pat. No. 5,100,241, WO 99/67015 A1, EP 1 020 167 A2, U.S. Pat. No. 5,586,821, EP 1 016 452 A2, DE 36 40 279 A1, WO 94/26403 A1, EP 0 692 229 A1, EP 1 005 901 A2, U.S. Pat. No. 5,344,232.
As a refinement, cementing systems have both the cement powder and the monomer liquid prepackaged in separate compartments of the mixing systems and have them mixed with each other only right before the application of the cement in the cementing system (U.S. Pat. No. 5,997,544, EP 0 692 229 A1, U.S. Pat. No. 6,709,149 B1). One issue of these systems is the transfer of the monomer liquid into the cement powder and complete mixing of these two components in order to obtain a homogeneous cement dough, which, in particular, must not contain any clusters of cement powder that has not been wetted by the monomer liquid. The Optipac™ full-prepack mixing system (Biomet Switzerland), which currently is commercially available in Europe, has simple tubes attached on the side in the lower part of the cartridge, which tubes penetrate through the cartridge wall and aspirate the monomer liquid from aluminium compound bags into the cement powder, approximately into the middle of the cement powder, through the action of a vacuum.
Aluminium compound bags have been known for packaging and storage of monomer liquid only for a few years. Very good experience in terms of the storage properties has been made with glass vials. Glass vials have been used for decades for conventional polymethylmethacrylate bone cements with good success. Aside from the perfect absence of leakage, glass vials are also advantageous in that they can be manufactured in large numbers at low prices. It is therefore reasonable to use glass vials for packaging and storage of monomer liquid in prepack vacuum cementing systems.
DE 195 32 015 A1 describes a device for mixing and dispensing multi-component products. What is proposed therein is a device for vial opening that is based on a bearing socket about which a vial holder can move in a rotating manner being provided on the outside of the cement cartridge. The head of the vial is situated on the inside of the bearing socket. Rotation of the vial holder about the bearing socket shears the vial head off the vial body. Then, the liquid from the vial can be transferred into the cartridge through an opening in the cartridge wall.
WO 97/18031 A1 proposes a device in which a vial is punctured on its bottom and the monomer liquid can subsequently flow through the hollow mixing rod into the cement cartridge.
A system for vial opening in the case of cementing systems is disclosed in EP 1 031 333 A1. In this system, a motion of the mixing rod with respect to a wedge-shaped device in the cartridge head moves the vial head transverse with respect to the vial axis, whereby the vial head is sheared off the vial body. Problems encountered in this regard include the relatively complex structure of the opening device and the risk of the wedge-shaped device getting lodged.
WO 2010/012114 A1 describes a device for opening vials. Analogous to DE 195 32 015 A1, this concerns a rotation mechanism for shearing off the vial head. The only difference from DE 195 32 015 A1 is that a rotation socket is moved with respect to the vial holder rather than the vial holder being moved with respect to the rotation socket as is the case in DE 195 32 015 A1.
The essential disadvantage of the opening devices presented in the unexamined German applications cited here is that moving mechanical parts are needed which may become lodged and whose manufacture must meet relatively high manufacturing tolerance standards in order to ensure operability.
A generic opening device is known from EP 0 079 983 A1, in which a glass vial is supported in a pressure-resistant external container and the head of the glass vial can be sheared off through the motion of a safety valve that reaches into the external container. For this purpose, the safety valve comprises an elastic sealing cuff and a pot-like lower part that reaches into the head of the vial in order to reliably shear it off. In addition, the safety valve comprises on its outlet channel means, for example a helical spring, for actuation of the safety valve.
Although the vial is very easy to open as a result of this structure, the complex structure of the safety valve including a multitude of single components is disadvantageous. This, for one, leads to increased costs in association with the manufacture of an opening device of this type, and, on the other hand, the vial may be opened inadvertently during the manufacture of said opening device.
The object of the invention is to develop a robust and simple device for storing and opening monomer vials of vacuum cementing systems for polymethylmethacrylate bone cements that are pre-filled with cement powder and monomer liquid and can be provided to the medical user in the form of prepack vacuum cementing systems. The device is to consist of a minimal number of components and be inexpensive to manufacture. Moreover, manufacture should be feasible reliably without the risk of destroying the vials. The device must be usable rapidly and safely for opening monomer vials by a user without any previous special knowledge. The device must not be associated with a risk of lodging while the vial is being opened.